sairiyou wo suru to, sigen wo mamoremasu.

A natural reading is:

さいりよう を すると、しげん を まもれます。

Without spaces, it is normally written:

再利用をすると、資源を守れます。

Word readings:

• 再利用 = さいりよう
• 資源 = しげん
• 守れます = まもれます

再利用 means reuse or recycling/reuse as a noun.

When you add する, it becomes a verb:

• 再利用する = to reuse / to recycle / to make use of again

So:

• 再利用をする literally means to do reuse

In modern Japanese, 再利用する is often more natural and compact than 再利用をする, but both are grammatically correct.

So this sentence could also be written as:

再利用すると、資源を守れます。

Because 再利用 is a noun here, and する is the verb to do.

Japanese often makes verbs from nouns this way:

• 勉強をする = to study
• 掃除をする = to clean
• 再利用をする = to reuse

The particle を marks the noun as the thing being done.

However, with many suru-verbs, the を is often omitted in ordinary writing and speech:

• 勉強する
• 掃除する
• 再利用する

So 再利用をする and 再利用する both work.

Here, と means something like:

• when
• if
• whenever

In this pattern, X と、Y, it often expresses a natural consequence or general result:

• 再利用をすると、資源を守れます。
• If/when you reuse things, you can protect resources.

This と is commonly used for statements like:

• 春になると、暖かくなります。
  When spring comes, it gets warm.
• このボタンを押すと、ドアが開きます。
  If you press this button, the door opens.

So here it is presenting reusing as something that leads to protecting resources.

守れます is the potential form of 守る.

• 守る = to protect
• 守れます = can protect / be able to protect

So:

• 資源を守ります = (someone) protects resources
• 資源を守れます = (someone) can protect resources

The sentence is saying that by reusing, it becomes possible to protect resources.

This often sounds a little softer or more practical in Japanese, like saying:

• Reusing helps us protect resources
• By reusing, we can protect resources

It comes from the verb 守る, which is a godan verb.

Formation:

• dictionary form: 守る
• potential form plain: 守れる
• polite potential: 守れます

So:

• 守る → 守れる → 守れます

This same pattern appears in other -u verbs:

• 書く → 書ける → 書けます
• 話す → 話せる → 話せます
• 読む → 読める → 読めます

Japanese often leaves the subject unstated when it is obvious, general, or unimportant.

So 再利用をすると、資源を守れます。 does not explicitly say:

• we
• you
• people

Depending on context, it could mean:

• If we reuse things, we can protect resources.
• If you reuse things, you can protect resources.
• By reusing, people can protect resources.

This omission is very normal in Japanese.

Because 資源 is the direct object of 守れます.

• 資源 = resources
• を marks what is being protected
• 守れます = can protect

So:

• 資源を守れます = can protect resources

This is the standard object marker.

Grammatically, it means can protect resources.

In Japanese, the potential form of a transitive verb often keeps を:

• 本を読めます = can read books
• 日本語を話せます = can speak Japanese
• 資源を守れます = can protect resources

Sometimes learners expect something more like a passive meaning, but here it is straightforwardly be able to protect.

In natural English, the whole sentence is often best understood as:

• By reusing things, we can protect resources.

A sentence does not always need は.

Here, the structure is simply:

• 再利用をすると = if/when one reuses
• 資源を守れます = one can protect resources

Japanese often leaves out a topic if the sentence is a general statement.

You could add a topic in a larger context, for example:

• 私たちは、再利用をすると、資源を守れます。
  As for us, if we reuse things, we can protect resources.

But in a standalone general statement, leaving it out sounds natural.

Often, yes.

Both are correct, but 再利用すると is a little more streamlined because 再利用する is commonly treated as a single suru-verb.

Compare:

• 再利用をすると、資源を守れます。
• 再利用すると、資源を守れます。

The second version is a bit more compact and often feels more natural in everyday usage.

Still, the original sentence is perfectly understandable and grammatical.

再利用 literally means reuse or use again.

Depending on context, English might translate it as:

• reuse
• recycling
• reutilization

But strictly speaking:

• 再 = again
• 利用 = use

So the core idea is using something again.

If the lesson meaning already says recycling, that may be the intended practical meaning, but the Japanese word itself is closer to reuse/reutilization.

Those spaces are usually just for learners.

Normal Japanese is written without spaces:

再利用をすると、資源を守れます。

Textbooks or beginner materials sometimes add spaces to help learners see:

• word boundaries
• particles
• sentence structure

So the spaces are not part of standard Japanese writing.